1. Field of the Invention
This invention relates to a counter circuit operable in synchronism with a frame of a digital data signal, so that a frame synchronization of the counter circuit with the frame in the digital data signal can be properly achieved even if a frame synchronization signal of the digital data signal is not available due to a dropout or the like.
2. Prior Art
In a compact disc of the compact disc digital audio system, information is stored in the compact disc in units called frames each composed of 588 channel bits. As shown in FIG. 1, one frame is composed of one (1) control signal symbol, 24 data symbols and 8 parity symbols. The frame contains a synchronization pattern at its front end for detecting leading bit points of the control signal symbol and a foremost one of each of the data symbols and parity symbols. This frame synchronization pattern is a so-called 11T-11T pattern composed of 11 consecutive channel bits representing "1" and 11 consecutive channel bits representing "0" and following them as shown in FIG. 2, and this frame synchronization pattern is separate from the row of data of the frame. The frame synchronization pattern is detected to produce a frame synchronization signal based on which the number of bits of the frame is counted to detect the control signal symbol and the foremost one of each of the data symbols and parity symbols. Therefore, if a data error develops in the frame due to damage to the disc or the like, and the frame synchronization pattern can not be detected, which is commonly referred to as "dropout", then the data can not be properly reproduced from the disc.